1. Field of the Invention
The present invention is directed to throttling and shut-off valves for slurry transporting pipelines and conduits. More particularly, the present invention is directed to throttling and shut-off valves for pipelines and conduits which transport relatively coarse slurries of abrasive solid particulate materials.
2. Brief Description of the Prior Art
Pipelines and conduits which transport slurries of solid particulate materials suspended in a fluid, usually liquid, carrying medium, are well known. In fact, during the recent years transportation of ground coal and other minerals in the form of aqueous, or occasionally liquid hydrocarbon based slurries has gained increasing acceptance in the energy, mining and related industries. In one type of slurry pipeline or transportation system, the coal or other mineral slurry is transported relatively short distances, for example from a mine to a nearby processing plant. In another type of slurry pipeline, minerals or coal, principally coal, is transported long distances, for example from a remote mine to an industrialized or densely populated area where the coal is to be used as an energy source.
Transporting coal and other minerals in the form of slurries, however, presents certain difficult problems with regard to wear of certain components of the pipeline and associated equipment. Pipe elbows, pumps and throttling and shut-off valves are especially wear-prone and therefore have relatively short service lives, particularly when the solid material transported as a slurry is coarse or abrasive, or both. In this regard it is noted that most mineral slurries are abrasive. Moreover, a slurry is usually considered coarse if the average particle size in the slurry exceeds approximately 1 to 2 milimeters.
Throttling and shut-off valves for coarse or abrasive slurries have been, by-and-large, limited in the prior art to gate type valves and ball valves. These valves, however, are not sufficiently abrasion resistant, and also cause an undesirable, relatively large loss of energy in the slurry flow.
Another type of slurry throttling and shut-off valve commonly used in the prior art is the elastomeric sphincter type valve, which functions relatively well for throttling the flow of fine slurries even when the solid material of the slurry is abrasive. The sphincter type valves, however, wear and deteriorate rapidly when used in pipelines transporting coarse slurries where the suspended solid material contains abrasive, sharp edged particles.
In light of the foregoing, there is a definite need in the prior art for throttling and shut-off valves of increased wear and abrasion resistance for slurry pipelines and slurry transporting conduits, particularly ones which minimize energy loss in the valve. The present invention provides such throttling and shut-off valves. U.S. Pat. Nos. 2,507,851; 2,240,119; 2,403,751; 2,882,967; 4,231,389, and 4,275,763 disclose valve or related structures which are of interest as background to the valve assembly of the present invention.